1. Field of the Invention
The invention relates to a method of manufacturing a semiconductor device, particularly, a method of manufacturing a semiconductor device having an ultraviolet erasable nonvolatile memory cell.
2. Description of the Related Art
An ultraviolet EPROM (Erasable Programmable Read-Only Memory) is a memory where electrically written data is erasable by ultraviolet irradiation, and is formed on a semiconductor substrate by itself or by being integrated into other semiconductor integrated circuit, for example, a microcomputer.
A silicon nitride film as a passivation film and a polyimide film as a buffer against stress of a package are often formed on a semiconductor substrate formed with this EPROM. However, these silicon nitride film and polyimide film have a property of not transmitting ultraviolet light, the data erasing of the EPROM is not achievable if these are left on the EPROM region. Therefore, these films on the EPROM region are removed by etching. For reducing the number of processes, the removing of these films on the EPROM region by etching is performed at the same time as when a silicon nitride film or the like on pad electrodes for wire bonding is removed by etching. An ultraviolet EPROM is described in Japanese Patent Application Publication No. 2005-243127.
When the silicon nitride film or the like on the pad electrodes is removed by etching, however, over-etching is performed for exposing the pad electrodes completely. This causes an interlayer insulation film to be etched to expose a wiring layer under the pad electrodes in the EPROM region. When the wiring layer is exposed, the reliability of the EPROM is degraded by water infiltration or the like. Furthermore, since the exposed wiring layer is damaged by etching, the resistance of the wiring layer changes.